This application relates to a method of desizing or removing an intermediate coating from ceramic or glass fibers.
Ceramic and glass fibers are utilized in the formation of ceramic matrix composite (“CMC”) materials. CMC materials are finding applications in any number of high temperature applications. As an example, gas turbine engines may incorporate a number of components formed of CMC materials.
The CMC materials are formed from ceramic or glass fibers, such as silicon carbide (“SiC”) fibers. In the formation of CMC materials, the diameter of the fibers may be between 5 and 150 microns. Such fibers are provided with a polymeric coating, also called a sizing, which prevents fiber breakage and damage during handling after production. However, in the process of making the CMC materials, it is often desirable to coat the SiC fibers with one or more fiber interface coatings. As an example, an interface coating such as boron nitride on a SiC fiber provides for a weak interface in the CMC material which deflect cracks and provides toughness in the material. Outwardly of this coating, there could also be another coating such as silicon nitride, silicon carbide, boron carbide, carbon, or combinations thereof, which improves the environmental durability of the underlying boron nitride coating.
Prior to application of the interface coating or coatings, the polymer sizing on the fibers must be removed, or desized.
Traditionally, the desizing of fibers such as SiC has been provided by using a high temperature ammonia heat treatment. In some instances, other methods such as passing the fibers through a flame have also been used to burn off the polymer coating and desize the fiber. For textile sizes and applications, hot water treatments have also been utilized.